The present invention relates generally to Voltage controlled oscillators (VCO""s). A VCO with enhanced Q and better signal to noise ration (SNR) is disclosed.
Voltage Controlled Oscillators (VCO""s) are important components in wireless communication systems. FIG. 1 is a block diagram illustrating a conventional differential cascaded VCO with an LC tank. The output of stage 102 is input to stage 104 and the output of stage 104 is input to stage 106. The output of stage 106 is negatively fed forward to the input of stage 102 with the positive output being fed into the negative input and the negative output being fed into the positive input. The cascaded stages produce a filtering effect with somewhat improved phase noise, but the circuit tends to consume a large amount of current.
It would be desirable if an improved cascaded VCO could be developed with low phase noise so that the signal to noise ratio in the output signal can be reduced. Furthermore, it would be desirable if the amplitude could be increased without increasing the current drawn by the device.
An improved cascaded VCO is disclosed. In one embodiment, each oscillator stage receives an additional input from a second stage in addition to the conventional input received from a previous stage. The inputs are selected with a phase relationship that causes the total input signal power to each stage to be increased.
It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, a method, or a computer readable medium such as a computer readable storage medium or a computer network wherein program instructions are sent over optical or electronic communication links. Several inventive embodiments of the present invention are described below.
In one embodiment, a cascaded voltage controlled oscillator includes a first oscillator stage having a first oscillator stage first input, a first oscillator stage second input and a first oscillator stage output. A second oscillator stage includes a second oscillator stage input and a second oscillator stage output wherein the first oscillator stage output is input to the second oscillator stage input and wherein the second oscillator stage output is fed back to the first oscillator stage second input. A third oscillator stage includes a third oscillator stage input and a third oscillator stage output wherein the second oscillator stage output is fed to the third oscillator stage input.
These and other features and advantages of the present invention will be presented in more detail in the following detailed description and the accompanying figures which illustrate by way of example the principles of the invention.